1. Field of the Invention
The present invention relates generally to small particle copper pyrithione compositions, and a method of preparing these compositions. Preferably the compositions are provided in a non-dusting form as a dispersion of the small particles in an aqueous or organic solvent carrier. Alternatively, the small particles are provided in the form of a solid powder for use in facilities equipped to avoid or minimize human exposure to, and handling of, the powder. The small particle copper pyrithione compositions are suitable for use as antifouling agents in antifouling paints, such as marine paints. These small particles exhibit enhanced storage stability in dispersions with liquid media, as well as an enhanced leach rate from the antifouling paints, relative to larger size copper pyrithione particles.
2. Description of the Related Art
Pyrithione salts are well known compounds that are useful in a wide variety of applications including their use biocides, such as fungicides and bactericides. Heavy metal salts of pyrithione, including zinc, tin, cadmium and zirconium, as well as the magnesium and aluminum salts, have been produced in the form of flat platelets suitable for use in shampoo, are disclosed in U.S. Pat. Nos. 4,345,080 and 4,323,683.
Small particles of metal salts of pyrithione have been disclosed for use on the skin and hair. Illustratively, U.S. Pat. No. 4,670,430 discloses polyvalent metal salts of 2-mercaptopyridine-N-oxide in the form of a fine powder of particles in which at least fifty percent of the particles have a particle size below 0.2 micron. The ""430 patent discloses that, when this fine particle of particles is incorporated into shampoo or rinse compositions, the dispersion stability of these salts is improved and the adsorbability of the particles onto the skin and hair is enhanced. Another illustration of the use of small particles of metal pyrithiones in hair treatment is provided in U.S. Pat. No. 5,723,112. The ""112 patent discloses an antimicrobial hair treatment composition comprising (a) a surfactant, (b) fine particles of an insoluble particulate metal pyrithione in which at least 90% by weight of the particles have a size of five microns or less, and (c) a polymeric cationic deposition aid for the small particles.
Pyrithiones have also been used as antimicrobial additives in a variety of paints. Illustratively, various paints containing a pyrithione salt (e.g. zinc or sodium pyrithione) plus a copper salt (e.g. cuprous oxide or cuprous thiocyanate) are known in the art, as disclosed, for example, in U.S. Pat. No. 5,057,153. As another illustration, U.S. Pat. No. 5,185,033 describes a process for making a paint or paint base containing copper pyrithione or pyrithione disulfide plus cuprous oxide, wherein the paint exhibits stability against gelation during storage. As yet another illustration, U.S. Pat. No. 5,246,489 discloses a process for providing in situ generation of copper pyrithione in a paint or paint base which comprises incorporating a metal salt of pyrithione, cuprous oxide and a controlled amount of water into the paint either during or after the formation of the paint.
In many applications, copper pyrithione offers several advantages over other forms of pyrithione such as zinc pyrithione. For example, copper pyrithione is more stable than zinc pyrithione when added to paint products, and therefore is less likely to cause gelation during storage.
Commercially available copper pyrithione is typically sold as a dry powder. Generally, the particle size range for this commercial dry powder is between about 0.8 micron and about 30 microns, with a median particle size of from 3 to 6 microns. A key disadvantage of this commercial powder is that it generates dust during handling, necessitating special handling equipment, particularly since copper pyrithione powder was shown to be more toxic than zinc pyrithione powder when tested for acute inhalation toxicity in rats. This dusting issue associated with copper pyrithione dry powder is addressed in PCT publication WO00/54589. This publication discloses resolving the dusting issue using dispersions of solid copper pyrithione in a liquid dispersing medium.
The present inventors have now observed that, in use, although the dispersions of the PCT publication WO00/54589 obviate the dusting issue, they are subject to another problem. More specifically, paints made with these dispersions tend to provide a decreased leaching rate of copper pyrithione out of the paint in a low temperature environment. Such decreased leaching increases the likelihood that not enough antifouling agent will leach from the paint to prevent marine fouling at the paint""s surface. The present invention provides one solution to this decreased leach rate problem, thereby insuring desired low temperature antifouling efficacy for copper pyrithione-containing antifouling paints.
In one aspect, the present invention relates to a composition comprising small particles of copper pyrithione having a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3 microns, these small particles exhibit enhanced antimicrobial performance, as compared to larger size copper pyrithione particles, in a marine paint that is exposed to a cold water environment of from about 5 degrees Centigrade to about 15 degrees Centigrade. In another aspect, the invention relates to a paint containing the small particles of copper pyrithione. In another aspect, the invention relates to a method for enhancing the antifouling efficacy of a paint in a cold water environment, said method comprising incorporating the small particles of pyrithione into the paint.
In another aspect, the present invention relates to a composition comprising a non-dusting copper pyrithione dispersion comprising small solid particles of copper pyrithione dispersed in a liquid dispersant. Preferably, the solid particles have a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3 microns. Optionally, the dispersion additionally contains a dust-inhibiting agent selected from the group consisting of surfactants, polymer resins, binders, and combinations thereof.
In another aspect, the present invention relates to a method of making a non-dusting dispersion of small solid particles of copper pyrithione dispersed in a liquid dispersant comprising the steps of:
(a) providing small solid particles of copper pyrithione within a desired size range of from about 0.1 to about 10 microns, and a median particle size of less than 3 microns, by subjecting larger solid particles of copper pyrithione to a force selected from the group consisting of grinding, milling, pulverizing, sonicating, and combinations thereof, and
(b) dispersing copper pyrithione particles in a liquid dispersant.
In yet another aspect, the present invention relates to a method of making a non-dusting dispersion of small solid particles of copper pyrithione dispersed in a liquid dispersant comprising the steps of:
(a) dispersing larger solid particles of copper pyrithione in a liquid dispersant to provide a liquid dispersion have said larger solid particles dispersed therein, and
(b) subjecting said liquid dispersion of copper pyrithione to a force selected from the group consisting of grinding, milling, pulverizing, sonicating, and combinations thereof, in order to reduce the size of said larger size particles in said dispersion within a desired size range of from about 0.1 to about 10 microns, and a median particle size of less than 3 microns.
In still another aspect, the present invention relates to a method of enhancing the antifouling characteristics of a paint which comprises adding to the paint an antifouling effective amount of solid particles of copper pyrithione having a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3.0 microns.
In yet another aspect, the present invention relates to a method of enhancing the antifouling characteristics of a paint which comprises adding to the paint an antifouling effective amount of a non-dusting copper pyrithione dispersion comprising small solid particles of copper pyrithione dispersed in a liquid dispersant, said solid particles having a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3.0 microns.
In still another aspect, the present invention relates to an antifouling paint comprising a paint base and an antifouling effective amount solid particles of copper pyrithione having a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3.0 microns.
In yet another aspect, the present invention relates to an antifouling paint comprising a paint base and an antifouling effective amount solid particles of copper pyrithione having a particle size within a range of from about 0.25 to about 7 microns, and a median particle size of less than 2 microns.
In still another aspect, the present invention relates to a method of enhancing, in a cold water marine environment, the leach rate of copper pyrithione from a copper pyrithione-containing paint, said method comprising incorporating into the paint solid particles of copper pyrithione having a particle size within a range of from about 0.1 to about 10 microns and a median particle size of less than 3 microns, in order to provide a copper pyrithione leach rate from the paint of at least one microgram per square centimeter per day of exposure of said paint to said cold water marine environment when measured at a cold water temperature of 10.6 degrees Centigrade.
In yet another aspect, the present invention relates to a copper pyrithione-containing antifouling paint providing an enhanced rate of leaching of the copper pyrithione from the paint in a cold water marine environment, said paint comprising a paint base and an antifouling effective amount of solid particles of the copper pyrithione, said solid particles having a particle size within a range of from about 0.1 to about 10 microns, and a median particle size of less than 3 microns, said solid particles having a leach rate from the paint of at least one microgram per square centimeter per day of exposure of said paint to said cold water marine environment when measured at a cold water temperature of 10.6 degrees Centigrade.
These and other aspects of the present invention, will become apparent upon reading the following detailed description of the invention.